The present invention provides piperazine derivatives of formula as well as pharmaceutically acceptable salts and esters thereof, wherein R1 to R5 have the significance given in the description. 906 gcm3 and a Dow Rheology Index of at least 5MI2,MI2 being the melt index measured according to ASTMD-1238 condition 190\xb0 C. The new invention relates to the use of the theoretically ideal stability plane concept to provide natural stability in negative heel shoe soles that are less thick in the heel area than in the rest of the shoe sole. , and a molar ratio of mayenite to calcium hydroxide is 19. According to an embodiment, a system for providing voltage supply protection in a memory device is provided, the system including a memory array including a plurality of memory cells arranged in a plurality of groups of memory cells, and a plurality of current limiting elements, wherein each group of memory cells is associated with at least one current limiting element. That is, the intermediate routing node sends messages with challenge mechanism to the server, based on the response or otherwise, sends messages and anti-service attack downloads to the client devices and receives response.